Journal of Aerospace Engineering

A design method on scramjet nozzles is proposed to satisfy the requirements of nozzle positions and geometrical constraints. The proposed method adopts the inverse design concept and maximum thrust theory to achieve a good aerodynamic performance. The nozzle contours are generated by a universal method for solving partial differential equations: the method of characteristics. First, the principle of the proposed method is discussed, including the details of the implementation procedure. Second, the numerical simulation method adopted to obtain the flow field of the nozzle is briefly introduced. Then, the verification cases are conducted to validate the accuracy and effectiveness of the proposed method by comparing the flow conditions on two key points. The maximum relative error of the Mach number is only $-0.50\%$. The flow deflection angle exhibits a relatively more significant deviation than the Mach number, reaching approximately –1.46%. Overall, the proposed method can design the required nozzle with sufficient accuracy. Subsequently, the nozzle’s geometrical parameters in a previous study are adopted to design the nozzle using the proposed method. The aerodynamic performance, especially in the axial thrust coefficient, remains approximately constant. The comparison of the aerodynamic performance shows that the proposed method not only satisfies the requirement of high aerodynamic performance but also realizes the full geometrical constraints. This study provides an effective nozzle design method with high aerodynamic performance and full geometrical constraints, which can facilitate the airframe–engine integration.

The use of carbon nanotubes (CNTs) in augmenting the mechanical properties of fiber-reinforced laminated composites is a fact. In this paper, the semianalytical studies on the dynamic instability behavior and linear and nonlinear responses of a randomly distributed CNT and fiber-reinforced interlamina hybrid composite (CNTFRHC) plate with and without damping under time-dependent in-plane uniaxial uniform compression loading are presented. Each lamina of the laminate is made of multiscale materials such as CNT/polymer/fiber. The effective mechanical properties of the lamina are estimated in two steps. First, the Eshelby–Mori–Tanaka technique is used to compute the effective mechanical properties of randomly distributed CNTs in a polymer matrix (i.e., CNT-embedded matrix). Second, the effective mechanical properties of the CNT-embedded matrix reinforced with fiber (either carbon or glass) are estimated by using various homogenization techniques. The plate is modeled by using higher-order shear deformation theory (HSDT) and von Kármán nonlinearity. Governing partial differential equations of the CNTFRHC plate are obtained by Hamilton’s principle and reduced to Mathieu–Hill equations by using the Galerkin method. Mathieu–Hill equations are solved by the Bolotin method to trace the boundaries of the instability region corresponding periods $T$ and $2T$. Finally, the influence of different parameters such as CNT agglomerations, CNT mass fraction, edge-to-thickness ratio, compression preloading, boundary conditions, and damping on the dynamic instability region of the CNTFRHC plates are studied in detail. Numerical results provide useful insights into the selection of parameters with different combinations for the desired design of the CNTFRHC plate against instability. Furthermore, to know the characteristics of the instability region of a CNTFRHC plate such as the existence of beats, dependence on geometric nonlinearity, and forcing frequency for which the linear and nonlinear responses with and without damping in both stable and unstable regions are presented.

Due to different requirements of flight tasks, take-off weights vary according to different payloads, which will definitely influence the trim characteristics and flight dynamics of vehicles. When the mass ratio between the flapping wing and body increases to a certain value, it is necessary to regard flapping-wing microair vehicles (FWMAVs) as a multibody system, and the rigid-body model is no longer appropriate to be used as dynamic modeling. The flight dynamic stability analysis considering the oscillation of body, wing flexibility, and variation of take-off weight in forward flight is worthwhile to be studied. In this study, based on a method coupling three-dimensional computational fluid dynamics (CFD), computational structural dynamics (CSD), and multibody dynamic equations for FWMAVs, the dynamic and trim characteristics of systems with different take-off weights have been studied and compared. In addition, the dynamic stability has been analyzed and compared by three different methods including the averaged method, Floquet method, and direct time integration. Results show that with the increase of take-off weight, the FWMAV in forward flight changes from unstable (wing to body mass ratio is 8.5%) to stable (wing to body mass ratio is 6% and 7%). The transformation of stability mainly results from two contributions: the change of trim conditions and body oscillation. Furthermore, a direct time integration method has been used to address the impact of nonlinear effects. The results show that a nonlinear term does not change the qualitative results of stability but will change the specific evolution of state variables compared with a linear model. The quantitative results can give insight into the design of FWMAVs with different wing to body mass ratios.

In the present article, a displacement-based polynomial-type quasi-three-dimensional plate theory is developed and applied to predict the accurate thermomechanical bending behavior of sandwich plates with functionally graded (FG) skins and a homogenous isotropic core. The theory considers the effects of transverse shear and normal stresses. The $x$-directional and $y$-directional displacements consist of extension, bending, and shear components expanded up to fifth-order polynomials in terms of the thickness coordinates. The $z$-directional displacement consists of a transverse normal effect up to a fourth-order polynomial in terms of the thickness coordinate. The governing equations are extracted using the principle of virtual work, and thermomechanical bending solution for simply supported plates is obtained using Navier’s solution technique. The present results are compared with the previously published results and are found to be in good agreement with them.

In current galloping studies, the shape and surface of ice accretion are usually simplified to the regular and smooth properties, although they have the probability of irregularity and roughness in real conditions. To study the effect of these two factors on galloping stability, high-frequency force balance (HFFB) wind tunnel tests were conducted to obtain the aerodynamic characteristics of crescent-shaped iced conductor models with different ice surface roughness and ice shape. Furthermore, based on the Den Hartog and Nigol galloping mechanisms, the differences of galloping stability judgment are analyzed. Finally, a finite-element numerical simulation is also conducted to compare the galloping properties of iced conductors with rough and smooth surfaces. The results show that ideal crescent-shaped iced conductors with smooth ice surfaces are more prone to galloping compared with the rough ice surface condition, which is also verified by the results of the finite-element numerical simulation. Additionally, irregularities of the ice shape will result in a decrease of Den Hartog and Nigol coefficients in the negative value range, which means it is more likely to lead to the galloping phenomenon.

A computational study of a nano coaxial rotor with bioinspired blade motion was conducted at an ultralow Reynolds number to determine the principle of improving rotor performance via an induced unsteady mechanism. A flow solver was established based on the preconditioned compressible Navier–Stokes equations, a lower-upper Symmetric-Gauss-Seidel with pseudo time sub-iteration (LUSGS-τts) dual-time marching method, and an overset grid technique. The effect of different pitching rotors on the nano coaxial rotor performance was investigated. A pitching upper rotor slightly impacted the nonpitching lower rotor, whereas it significantly affected the pitching lower rotor. Four blade pitching frequencies were applied successively to the upper rotor to investigate the effect of pitching frequency on rotor performance. The results indicated that the greatest improvement in figure of merit occurred at a blade pitching frequency of 4/revolution. The figure of merit values for the upper rotor and lower rotor were 7.2% and 6.7%, respectively. The generation and evolution of the leading-edge vortex and trailing-edge vortex led to reattachment of flow in cases in which the rotor performance was improved.

During service, transmission lines (TLs) will be subjected to unbalanced longitudinal loads due to events such as conductor breakage, insulator failure, and sudden ice shedding, which may damage TLs and subsequently hinder reliable power supply. Although unbalanced longitudinal loads are considered in current design codes, damage to TLs still occasionally occurs. This paper reviews the literature from the last $20\mathrm{years}$ pertaining to the response of TLs induced by the abovementioned events and associated tower failures. It comprises four main sections in relation to the sources of large unbalanced accidental loads: conductor breakage, sudden ice shedding, insulator breakage, and tower failure. Structural analysis methods to investigate these accidents are reviewed, and the latest research progress on modeling tower failure is discussed. Chinese code, American code and International Electrotechnical Commission code are compared to analyze the differences in accounting for longitudinal loads in these codes. In the end, several recommendations are provided for future design and research to ensure the structural safety of TLs.

This work proposes an effective analytical solution to study the nonlinear buckling of functionally graded material (FGM) porous cylindrical shells subjected to external pressure and elevated temperature. Volume fractions of constituents are varied through the thickness direction according to power functional rules, and effective properties are estimated according to a modified rule of mixture. The porosities are evenly or unevenly distributed within the shell. Basic equations of a simply supported shell are based on first-order shear deformation theory, including von Kármán-Donnell nonlinearity, and solved using analytical solutions and the Galerkin method. To account for practical situations, temperature-dependent properties, together with the elastic constraint of edges, are included. The suggested form of two-term deflection overcomes mathematical difficulties and is suitable for shear deformation cylindrical shells. Numerical results indicate that porosities detrimentally influence the buckling resistance of pressurized shells. Furthermore, tangential edge constraints have slight and significant effects on critical buckling loads and the pressure bearing capacity of porous shells at normal and high temperatures, respectively. Besides being an innovative approach, the presented study aims to address practical aspects in engineering applications of pressurized porous shells.

This paper proposes an outlier ensemble based on the clustering technique to improve the identification accuracy of wind tunnel systems, which are very critical pieces of test equipment in the field of aerospace. The use of clustering has two objectives in our outlier ensemble, that is, generating diverse training subsets and improving the robustness of base detectors. By analyzing the data characteristics of wind tunnel systems, we propose a hybrid criterion to determine the most appropriate clustering algorithm and the corresponding clustering number. This criterion is constituted by a qualitative and a quantitative criterion. The qualitative criterion is implemented first to eliminate several candidates from alternative clustering algorithms. Moreover, the quantitative criterion is used to determine the ultimate algorithm. In addition, a robust base detector is also developed with the assistance of the selected clustering algorithm. Finally, we verify the proposed detection model in two ways. In an offline application, the model is verified through two system identification models. In an online application, it is verified only through the performance of outlier detection.

In this paper, flow and heat transfer in a blade trailing edge cooling channel with differently shaped pin fin arrays were investigated numerically in a Reynolds number range from 10,000 to 50,000. A novel internal structure, a drop-shaped pin fin array with varied chord-lengths, is proposed in order to improve the thermal performance of the cooling channel. The numerical method was validated by the experimental data in the open literature. The steady numerical simulation was carried out in conjunction with the $k\text{-}\omega$ shear stress transfer (SST) turbulence model for the periodic cooling channel. A hexahedral mesh with high quality was adopted for domain discretization to obtain high-precision results. To investigate the mechanism of pressure loss and heat-transfer enhancement, the velocity fields at different locations were studied in detail, and the friction factor and Nusselt number were obtained and analyzed comprehensively. It was found that the friction factor ratio ($f/f_0$) of the channel with drop-shaped pin fins is 32.5% lower than that with circular pin fins, and the thermal performance factor (TPF) is 7.6% higher. Compared with circular pin fins, the drop-shaped pin fins can significantly improve the overall thermal performance at relatively high Reynolds numbers. The research results show that the newly proposed cooling scheme has great potential in application in a real modern advanced gas turbine blade.

Real-time identification and monitoring of the railway track dynamic parameters are necessary to ensure the safe operation of the railway transportation systems. Traditional global structural parameter identification methods have the problem of low efficiency in identifying structural parameters of railway track dynamic systems. To tackle the inefficiency problem, this paper proposes a new parameter identification method for railway track systems on the basis of the substructural identification algorithm. First, the railway track system is divided into several substructures depending on the vehicle loads. The parametric expression of the interface forces of the target substructure is constructed by the Chebyshev polynomials. Then, the sensitivity of the dynamic responses to the structural parameters and the interface force parameters can be obtained. The substructure parameters and the load parameters are identified simultaneously by the coupled iterative optimization algorithm based on the sensitivity analysis. The proposed substructural identification method greatly improves computational efficiency in the iterative process of parameter identification because the proposed method significantly reduces the number of parameters to be identified. Finally, a numerical example for a railway track dynamic system is employed to demonstrate the effectiveness of the proposed substructural identification method. The results from the numerical study show that changes in the structural parameters of rail track systems can be accurately identified using the proposed substructural identification method.

This paper considers the spacecraft formation flying (SFF) with a desired attitude. Two control problems are studied. One is the formation control of multiple spacecraft and the other is the attitude synchronization of multiple spacecraft. To solve the two problems, a 6-DOF model is adopted for each spacecraft. In the 6-DOF model, it is assumed that the inertia parameters are not well known and there are perturbations of orbitals, gravity, etc. With the aid of the backstepping technique and the algebraic graph theory, distributed robust control laws are proposed for the formation flying and attitude synchronization problems, respectively. The effectiveness of the proposed controllers is shown by simulation.

Transmissibility function (TF) is a useful damage indicator for effective structural damage detection (SDD) under unknown external excitations. However, TF is not sensitive enough to structural damage under measurement noise. To improve the sensitivity of this indicator, a common model reduction technique, that is, the system equivalent reduction expansion process (SEREP) was first adopted to obtain reduced element stiffness matrices in the initial analytical finite-element model of a structure; this was used to weight the TFs in this study. Then, inspired by the cosine similarity measure, a novel damage indicator, called the weighted transmissibility assurance criterion (WTAC), was proposed for evaluating structural states. The effectiveness of the proposed damage indicator, WTAC, was first studied by a six-story frame in numerical simulations. The results showed that the TF weighted by the reduced element stiffness matrices improved the signal-to-noise ratio of the TF, and the proposed WTAC detected changes in structural states under noise. Moreover, further experimental studies on an aluminum alloy frame were conducted in order to assess the proposed WTAC. The results indicated that the proposed WTAC may provide a potential tool for effective SDD with strong robustness and stability for long-term monitoring on site.

Aerodynamic shape optimization plays a significant role during the conceptual design stage of hypersonic vehicles. In this study, an interval-robust optimization method is proposed for the design of hypersonic vehicles, which integrates the tolerances of geometric variables under multiple flight conditions. Applying the class and shape transformation (CST) method, the wing of a representative hypersonic vehicle is modeled with relatively few geometric parameters containing physical meanings. By virtue of engineering methods, aerodynamic forces and heating properties of the hypersonic wing can be evaluated rapidly. The interval vectors are given to quantify geometric parameters considering the production and manufacturing tolerances. Subsequently, based on the Taylor series expansion method, the upper and lower bounds of aerodynamic forces and heating properties are obtained successfully. Unlike the deterministic aerodynamic shape optimization formulation, an interval-robust optimization strategy is presented by taking into account the nominal value and interval radius of aerodynamic forces and heating properties. Owing to the weighted processing, multipoint interval-robust optimization method (MP-IROM) is proposed to consider the multiple flight conditions. Two engineering examples are provided to demonstrate the feasibility and effectiveness of the proposed method in regards to optimizing the aerodynamic shape of a representative hypersonic vehicle wing.

Moving force identification (MFI) plays an important role in monitoring moving vehicle loads acting on a bridge, which has attracted great attention in recent years. Although many MFI methods have been proposed, their effectiveness in real bridges has not been carefully investigated. In this study, focusing on how to identify moving forces from structural responses in a real bridge, some important aspects are conducted and discussed in detail. The effectiveness of a MFI method based on dictionary expansion and sparse regularization is evaluated by a five-span continuous bridge in real engineering. First, a finite-element (FE) model is established to approximately describe the real bridge. Then, the FE model is updated based on the modal information obtained from structural responses, so the transfer matrices between moving forces and structural responses can be calculated. Meanwhile, data preprocessing is conducted and a suitable dictionary is designed to obtain reasonable MFI results. As a result, the MFI equation by adding reweighted $l_1$-norm regularization is used for MFI. Finally, two trucks with known gross vehicle weights are adopted to evaluate its effectiveness. The MFI results show that this method can reasonably estimate the moving vehicle loads acting on bridge deck, and the identified moving forces are reasonable.

This paper presents a method for stochastic deterioration modeling and fatigue damage assessment for composite wind turbine blades operating in offshore environments. The fatigue damage of the composite blades is analyzed and assessed based on the estimates for the applied loads along the blade span, stress analysis, fatigue crack evolution, and lifetime probability of fatigue failure. The complex stress states of the blade are mainly caused by the aerodynamic loads generated by corrected blade element momentum theory, gravity loads, and centrifugal loads. The fatigue of the wind turbine blade is then investigated on the basis of the actual fatigue damage propagation process. The stochastic gamma process is introduced to calculate the probability of fatigue failure of the blade for various critical limits, and these results together with lifecycle cost analysis are employed to determine the optimum maintenance strategy. Finally, a numerical example for a National Renewable Energy Laboratory 5-MW wind turbine blade is adopted to demonstrate the applicability of the proposed method. The numerical results show that the proposed approach can provide a reliable tool for estimating stress states, evaluating fatigue damage, analyzing lifetime fatigue failure probability, and optimizing repair time of the composite wind turbine blade.

The goal of this study was to characterize the effect of propeller variables as relevant to the design of a flight vehicle with numerous distributed propulsors. The impact of propeller radius, quantity, airfoil section characteristics, and blade count is examined. The test case is a small general aviation aircraft evaluated at a condition corresponding to cruise, such that thrust is constrained and propeller slipstream effects are negligible. From the perspective of power required, a minimal number of large-radius propellers are preferable. Increasing the number of propellers or blade count reduces the individual loading on each blade, which can lead to a significant drop in efficiency if the airfoil characteristics of the blade’s section are not well matched to the operating conditions. Reducing propeller radius is associated with a reduction in estimated range and endurance for a battery-powered aircraft.

The attitude tracking form quaternion measurements for a three-axis stabilized liquid-filled spacecraft are studied under uncertain parametric and external disturbances. The sloshing liquid inside the partially filled liquid tank is equivalent to a spherical pendulum model; thus, coupled dynamic equations are derived using the conservation of moment of momentum. Considering the failure of acceleration sensors, when the angular velocity information cannot be obtained, an adaptive robust backstepping control algorithm is proposed by combining the adaptive backstepping control technique with a passive control algorithm. A nonlinear damping algorithm is introduced to enhance the disturbance attenuation ability and robustness performance against lumped disturbances. Globally uniformly ultimately bounded (GUUB) stability of the entire closed-loop system is guaranteed based on the Lyapunov approach. The comparative simulations show that the control strategy is robust and effective for the spacecraft attitude maneuvers.

A main design consideration for spacecraft destined to operate in the meteoroid or orbital debris (MOD) environment is the prevention of possible damage that might occur following an MOD impact. Risk assessments that are performed during spacecraft design typically consider what might happen following an onorbit MOD impact. In order to perform such an assessment, a variety of response prediction equations are required, including equations that predict whether a structural element, such as a pressure vessel or fuel tank, is perforated or ruptured by an MOD impact. In this paper, we bring together the datasets from room temperature gas-filled and cryogenic liquid-filled pressure vessel testing programs to develop a single equation that predicts whether tank rupture will occur following a high-speed impact. A comparison with test results shows that the equation developed correctly predicts the rupture/nonrupture responses of the pressure vessels considered in this study. This new rupture limit equation (RLE) can now predict whether or not a composite overwrapped pressure vessel (COPV) would rupture under a much wider range of temperatures, constructions, and COPV contents.

The Moon has been the focus of several space exploration programs worldwide because it has valuable materials that could be mined and is suitable for a relay station to Mars. To realize long-term and large-scale crewed lunar exploration, a particle-size classification technology should be developed to achieve efficient in situ resource utilization. As conventional classification technologies that use airflow are not suitable for operations on the Moon, the authors have developed a new technology utilizing the Brazil nut effect in an inclined vibrating tube. Large particles included in the lunar regolith were susceptible to a downward fall in the inclined vibrating tube, and small particles were transported upward; thus, large and small particles were separated. It was demonstrated that particles with a diameter larger than 100 μm were separated from the bulk of the regolith and transported downward when the tube inclination angle was 20°. Conversely, small particles were selectively transported upward when the tube inclination angle was 30°. When the inclination angle was less than 20°, almost all particles were transported upward, and when it exceeded 30°, almost no particles were collected at the upper outlet, and almost all particles fell downward. This system is potentially efficient and reliable for lunar exploration because it is simple and does not require consumables, such as air and water.